This study investigated the factors related to betting impulsively on sports. Participants included 1816 adult sports bettors living in Australia. Nearly all participants said they had placed bets on impulse within the last 12 months. Those who made impulsive bets tended to gamble more frequently and have more severe gambling problems. They were more likely to have a shorter history of sports betting, suggesting that they might be inexperienced sports bettors. Also, they favoured micro-bets during a match over betting on the final outcome. Females were more likely than males to make impulsive bets before a match, and just as likely to make impulsive bets during a match. Health promoters should create problem gambling prevention campaigns that educate gamblers about the dangers of betting on impulse.